Disconnects of various types have been used in the past in various facets of well completions. These disconnects have been used in conjunction with wireline operations, and one known type of wireline disconnect is illustrated in U.S. Pat. No. 5,363,921. Other types of disconnects, such as Bowen Safety Joints, have been used which disengage by left-hand rotation at approximately 40% of the tool's right-hand make-up torque. The problem with use of disconnects that involve shear pin or twist-to-the-left release is that they are perceived as weak and, therefore, disadvantageous for use in drilling operations. During drilling operations, reverse torques can occur, for example, as reaction forces when using a downhole motor to power a bit. Other disconnects involve the use of a tool known as a "string shot," which is positioned adjacent a portion of the string and uses explosives to loosen up a particular joint, with the intention that upon a turn to the left, the joint adjacent to where the string shot is actuated will release.
During drilling operations, known designs of disconnects have several limitations. The disconnects are perceived to be weak points in the drill string because they employ such release mechanisms as shear pins or threads that turn to the left to release. Some even advertise this weak point feature, such as the coiled tubing release joint offered by Dowell Schlumberger. During drilling operations, severe loads are placed on the drill string which can result in an inadvertent release of such known release tools; hence, they are generally not used in drilling operations. However, should problems develop during the drilling operation, it is desirable to have a disconnect to facilitate removal of the drill string so that fishing operations or milling operations can be commenced, if necessary.
One of the limitations of prior tools has been the inability to transmit torques which are frequently encountered during drilling operations. Designs that use collets are prone to failure of such locking mechanisms in the disconnect under application of severe torque.
Hydraulic disconnects have been in use in thru-tubing fishing operations. One such design is a hydraulic disconnect product No. 379-70, made by Baker Oil Tools under Model No. FA/FAU, which uses a collet to hold a joint together and a ball to move a sleeve to unsupport the collet for a release. One of the difficulties in such joints is their potential to bind if, as they are being released, there is a significant tensile or compressive load applied to the connection.